Daniel Cawrey writes, in Firefox
Competitive Strategy Must Focus On Privacy,
Since Firefox is the only truly open browser and
its features do not depend primarily on investor
concerns, Mozilla has a unique opportunity to go to
great lengths protecting the privacy of its users
while they are on the Internet.

That's a great idea. How about a compromise?
Instead of dropping User-Agent entirely, minimize
it to a single common string, one that contains the
commonly sniffed information. Start with a privacy
option to enable this minimal User-Agent, and give
sites a chance to fix their sniffing when the early
adopter privacy-hawk users turn it on. When it works
for the privacy freaks, make it the default.